This invention relates generally to radar signal processing and more particularly to a system for providing sensitivity time control using range gated feedback.
Ground mapping radar has its own distinct parameters within which it must function. These parameters are distinct and vary in many facets from similar requirements of searching and tracking radar.
In a ground mapping radar system the strength of the reflection from the ground target depends upon the range, target reflectivity and antenna gain. Target reflectivity is normally a function of the grazing angle, which in turn is a function related to the range and aircraft attitude. Antenna gain is a function of what is referred to as the "tilt angle" and the "look down" angle, both of which are functions of the range. A sensitivity time control circuit has as its purpose the controlling of radar receiver gain as a function of range, to provide a uniform response from equal size targets. In currently available radar receivers, the sensitivity time control (STC) is manipulated manually by the operator. The sensitivity time control has a gain control waveform which repeats every range sweep. It begins with a preselected high attenuation at the origin of the sweep and reduces the attenuation linerly as the range increases. Beginning attenuation is set manually by the operator, with some automatic compensation for aircraft altitude. The slope of the waveform is also set manually by the operator. Due to the interaction between these controls and the manual IF gain and the Video gain controls, it is very difficult to adjust the STC and gain controls correctly. In addition, the need for readjustment is frequent. This is particularly disadvantageous where the operator may also have to monitor television and infrared displays simultaneously.